Bearings are used in a wide variety of technical fields in order to support, guide, and reduce the friction of motion between different parts such as between fixed and moving parts.
The bearings may face very high load forces in some technical fields such as in the crane and wind turbine area.
The raceways of a blade bearing have to be hardened in order for the bearing to achieve acceptable sub surface fatigue properties. The normal way to harden the raceways is either by flame hardening or by induction hardening. The dominating hardening process in the industry is to either have a flame or induction tool that follow the circumferential of the bearing rings until the raceway have been hardened. Because the hardening tool only can harden a small section/fraction of the raceway at a time, the blade bearing manufacturer has to start at an arbitrary or well defined location on the bearing rings and then continue round the circumferential until the hardening tool is back to starting position.
Overlapping of the starting and finishing positions in the hardening process is not allowed in order to avoid annealing or tempering of the already hardened raceway or in order to avoid unpredictable material characteristics. As consequence hereof a small portion of the raceway is less hardened i.e. “soft spots” in the hardened raceway. The present understanding within the technical field of bearings is that the “soft spot” areas are so small that they have no influence on the bearing life.
However, this is not always the case and the object of the present invention is to establish bearing technique which provides a longer total life of a bearing.